1. Field of the Invention
Embodiments of this invention relate to the design, synthesis, fabrication, characterization, and use of new coatings including soluble precursor conjugated polymers and nanotubes or graphene sheets to form new nanocomposites and dispersions or formulations. The coatings maybe used to form thin films and/or to create patterned surfaces.
More specifically, embodiments of this invention relate to the design, synthesis, fabrication, characterization, and use of new coatings, where a soluble precursor conjugated polymer is able to aid in the dispersion and/or deaggregation of nanotubes and/or graphene sheets to form clear and stable solutions polymer coated nanotubes and/or graphene sheets to form new nanocomposites and dispersions or formulations. Being polymerizable, the solutions are suitable for film formation and patterning substrate surfaces and the resulting films and patterned surfaces are amenable to crosslinking, e.g., electropolymerized and/or oxidatively polymerized on a surface, as homogeneous crosslinked films. The films find utility as electrically conducting films, electro-optically active films, and in electropatterning thin film applications. The films and patterns find utility as electrically conducting films, electro-optically active films, sensing, solid-state devices and in electropatterning thin film applications.
2. Description of the Related Art
The discovery of carbon nanotubes (CNTs) and graphene sheets (G) with their combination of extraordinary physical properties and ability to be dispersed in various polymer matrices has created a new class of polymer nanocomposites. Polymer nanocomposites containing CNTs and graphene have received high interest due to their unique properties, such as adjustable electrical conductivity, robust thermo-mechanical properties, and the potential to create new materials with improved characteristics coupled with good chemical stability.
Graphene has recently attracted attention due to its novel electronic, mechanical and thermal properties that have been well documented. However, just as with the newly discovered allotropes of carbon, such as carbon nanotubes, the limited availability of graphene and the lack of known adequate processes to transform it into valuable commercial products have been the rate-determining steps in the evaluation of graphene applications. However, the exploitation of the unique properties of nanocomposites made of carbon nanotubes and/or graphene depends on the quality of their dispersion at the molecular level and the level of polymer-CNTs/graphene interfacial interactions and/or bonding through covalent bonding interactions and/or non-covalent interactions.
An important challenge remaining for CNTs and graphene utilization in commercial products is achieving homogeneous dispersion of individual CNTs and individual graphene sheets to accelerate the use of such dispersions in various applications and especially in large scale applications. At the same time, it is desirable that such dispersions be easily made into films or paenabling the electro-optical and thermo-mechanical properties of the CNT/graphene to be exhibited.
The manufacture of composites including carbon nanotubes and/or graphene require not only that carbon nanotubes and/or graphene sheets to be produced on a large enough scale, but also that they be incorporated and homogeneously distributed into various matrices. However, it is known that carbon nanotubes and graphene sheets are very hydrophobic and easily from irreversible agglomerates in polar solvents (in the absence of dispersing reagents) as a result of strong pi-pi (π-π) stacking and van der Waals interactions. Thus, various methods have been developed to stabilize these materials either by covalent modification or noncovalent modification using chemical agents such as aromatic molecules, surfactants, and polymers. Among those two strategies, the noncovalent modification is favored because it is more convenient to use and the electronic structure of CNTs and graphene sheets can be maintained.
The lack of dispersibility of graphite materials including carbon nanotubes and graphene in aqueous media and in organic solvents constitutes a significant barrier to the use of graphite materials. Thus, colloidal dispersions of oxidized graphite sheets are preferentially used in making composite materials. One such oxidized graphite is graphene oxide (GO), which is a graphene (G) material including oxygen functional groups, such as epoxide, —OH, and —COOH groups that make the graphene hydrophilic and, through electrostatic repulsion, are dispersible in polar solvents. Such dispersions may be stabilized by strong stirring or ultrasonication. Exfoliated GO may then be subjected to chemical or electrochemical reduction to obtain graphene as individual sheets typically using hydrazine as reducing agent. While the chemical reduction of GO resulted in significant restoration of sp2 carbon sites in the sheet, the reduction is unable to completely remove all the oxygen functionalities.
As the processing of CNTs is generally difficult due to their insolubility in most common organic solvents, only low weight/weight (w/w) or weight/volume (w/v) concentrations are usually obtained. It is necessary to obtain a homogeneous dispersion of CNTs in an organic solvent for film preparation. It is desirable to have a convenient and facile route for the formation of such homogeneous dispersions through solution mixing methods including a dispersant polymer and CNTs. One such approach, that has been commonly employed, is the direct grafting of small molecules or polymers on the surface of the CNTs, e.g. surface initiated polymerization (SIP). However, a drawback of SIP is a reduction in the electro-optical properties of the CNT. Another approach involves the use of non-covalently adsorbed initiators or end-grafted polymers on the surface of the CNT without disrupting the π-conjugation of the aromatic rings on the CNT.
While various methods for preparing composite materials including carbon nanotubes and/or graphene sheets have been proposed, they all suffer from certain drawbacks. Thus, there is a need in the art for methods for making compositions including carbon nanotubes and/or graphene sheets that are readily scalable, render homogeneous nanocomposites having unique properties and that do not suffer from the drawback of prior art methods. Patterning is also of high interest, because patterning surfaces can lead to more integration of these materials in devices and miniaturization.